1. Field of the Invention
The present invention relates to a resin lens made of a resin and a method of molding a resin lens, and more particularly, to a resin lens that is suitable for an objective lens (pickup lens) of an optical pickup device for an optical disc and a method of molding a resin lens.
2. Description of the Related Art
In recent years, for example, a resin lens made of a thermoplastic resin instead of a glass-molded lens has been used as an objective lens, which is used for an optical pickup device for the reading or writing of an optical disc such as a Blu-ray disc, DVD, and CD. The objective lens is molded by, for example, injection molding.
Further, the resin lens, which is used as the objective lens of the optical pickup device, includes, for example, an optical functional section that has an optical function such as a condensing function, and a flange section that is used for positioning and fixing the lens to an optical device. Meanwhile, for example, the flange section is formed in the shape of a flange on the outer periphery of the optical functional section.
Furthermore, since the resin lens used as the objective lens is disposed close to an optical disc, for example, the resin lens is mounted on the end of a mounting frame (pickup holder) on which the objective lens of the optical pickup device is mounted. In this case, for example, the optical functional section of the resin lens is disposed on the inner periphery of the mounting frame, the flange section is disposed on a frame part of the mounting frame, and the flange section is fixed to the frame part of the mounting frame by, for example, an adhesive or the like.
In this case, an annular portion of the flange section of the resin lens, which comes in contact with the mounting frame, functions as a reference face. The reference face of the flange section of the resin lens comes in contact with the mounting frame, so that the resin lens is positioned (for example, Japanese Patent Application Laid-Open No. 2004-191948).
Accordingly, the resin lens is designed so that the position or gradient (optical axis direction) of the resin lens is set when the reference face of the resin lens comes in contact with a corresponding receiving face to the mounting frame.
Further, an injection mold includes cavities, a sprue, runners, and gates. The cavities mold portions that form resin lenses, and a resin is injected through the sprue so that the cavities are filled with the resin. The resin is supplied to a plurality of cavities, which is provided to obtain a number of resin lenses, from the sprue through the runner. The gates are formed between the runners and the cavities. Accordingly, a molded product, which is extracted from the injection mold, is obtained by filling the sprue, the runners, the gates, and the cavities with a resin and hardening the resin by cooling. In order to obtain the resin lens, it is necessary to cut a gate section, which is formed at the gate and connected to the resin lens molded by the cavity, and to cut out the resin lens from the molded product. Meanwhile, since the gate section is generally formed at one position on the outer peripheral portion of the resin lens, the resin lens cut out from the molded product has a cut portion at one position on the outer periphery.
The cut portion may be used as a reference position in the circumferential direction of the resin lens.
Further, the outer edge of the resin lens basically forms a circular shape, but a part of a circle is deformed due to the cut portion.
In this case, the following resin lens has been known. In the resin lens, a linear portion having a shape, which is obtained by cutting the outer edge of the resin lens in a direction orthogonal to a radial direction, is previously formed at a portion, where the cut portion is formed, of the outer edge of the resin lens, that is, the outer edge of the flange section. The linear portion of the flange section is not formed by cutting the gate section, but molded by the shape that is previously formed in the mold for molding the flange section. The gate section is cut along the linear portion. In this case, since having a shape that is obtained by cutting the outer periphery of the circular resin lens along a straight line orthogonal to the radial direction, the linear portion is formed inside a virtual circle along the outer periphery of the resin lens. Accordingly, the cut portion of the gate section may not protrude from the virtual circle along the outer periphery of the resin lens, and a cutting mark of the gate section does not interfere with the mounting of the resin lens on the optical device.
Meanwhile, in a mold for the objective lens, the portion, which forms the optical functional section closer to the inside than at least the flange section, functions as an insert and is rotatable relative to the mold. That is, in an injection mold that includes a movable mold and a stationary mold and is opened when a molded product is extracted, at least a portion, which forms the optical functional section of the resin lens, of the cavity for molding the resin lens is provided in the stationary mold and the movable mold as a cylindrical insert.
Further, the insert is formed in a cylindrical shape and is rotatable. Accordingly, when the circular optical functional section is formed, it may be possible to adjust the rotation angle of the insert so that optimum optical performance is exerted by the rotation of the insert. Meanwhile, inserts are provided in both the movable mold and the stationary mold, and face each other. Accordingly, if the rotation angles of the pair of inserts are adjusted, there are possibilities that the error of the central position, other shape errors, and the eccentricity or gradient of the insert that is rotatably received in a hole of the holder of the mold with a clearance may be changed and the shape of the molded resin lens may be slightly changed, thereby causing difference in the optical property of the resin lens. Therefore, it may be possible to optimize the optical property by adjusting the rotation angle of the insert.
Further, in the resin lens that includes the optical functional section and the flange section, the central face of the resin lens, which forms at least the optical functional section, is formed by the forming face of the insert, and the flange section, which is closer to the outer periphery than the optical functional section of the resin lens, is formed by the forming face of a peripheral portion (holder) of the portion into which the insert of the mold is inserted. Accordingly, the reference face, which is formed on the flange section, is also formed by not the insert but the holder.
In this case, the clearance, which allows the insert to rotate, is formed between the insert and the holder. Due to the clearance, the axial direction of the insert is slightly misaligned from the axial direction of the hole into which the insert of the holder is inserted, so that the insert is slightly inclined (tilted). Further, the direction of the inclined insert is changed by rotating the insert. Accordingly, the surface shape of the optical functional section, which is formed by the forming face of the insert, is changed by the rotation of the insert.
In contrast, since the holder is not rotated, the shape of the outer surface of the flange section formed by the forming face of the holder is not changed even though the insert is rotated.
Accordingly, errors in manufacturing the mold or errors caused by the molding, and errors caused by the rotation of the insert are added to each other between the reference face molded by the holder and the optical functional section molded by the insert. For this reason, there is a possibility that an error of an angle between the reference face and the optical axis of the optical functional section may be increased, which interferes with the development of another resin lens having high accuracy.